Centrifugal fan



Jan. 29, 1935. H. F. HAGEN 1,989,413

CENTRIFUGAL FAN Filed Oct. 31,- 1929 2 Sheets-Sheet 1 /'N VE'N TOR ATTURNEY 1935. H. F. HAGEN 1,989,413

CENTRIFUGAL FAN 2 Sheets-Sheet 2 Filed Oct. 31, l929 Ill ,4 TTOENEYPatented Jan. 29 1935 UNITED STATES CENTRIFUGAL FAN Harold F. Hagen,Dedham, Mass., assignor to B; F. Sturtevant Company, Hyde Park, Mass., acorporation of Massachusetts Application October 31,

4 Claims.

The present invention relates to centrifugal fans and more particularlyto fans having provision for eflicient variation of output independentlyof the speed. A fan of this general type dis- 6 closed in my Patent No.1,846,863, dated February 23, 1932, employs vanes constructed andarranged to impart a controllable spin velocity to the fluid in thedirection of rotation of the rotor. The illustrated embodiment of theinvention of said application is a, fan provided with inlet scrolls andhaving curved vanes which may be adjusted to impart any desired degreeof spin velocity to the entering fluid. Such a fan is particularlyadapted for induced draft.

The principal object of the present invention is to provide a fan inwhich the fluid may be admitted directly from the atmosphere and whichhas provision for imparting a controllable spin velocity to regulate theoutput of the fan.

With these objects in view, the principal feature of the presentinvention comprises a fan having vanes adapted to be placed in the inletand constructed and arranged to pivot on generally radial axes. A fan ofthis type is especially useful for forced draft wherein the air isadmitted to the rotor directly from the atmosphere rather than throughinlet connections such as are em ployed in induced draft fans.

Other features of the invention consist of certain novel features ofconstruction, combinations and arrangement of parts hereinafterdescribed and particularly defined in the claims.

In the accompanying drawings illustrating the preferred form of theinvention, Fig. 1 is a side elevation of the improved forced draft fan;Fig. 2 is a section on line 2-2 of Fig. 1; and Fig. 3 is a diagrammaticplan view of a portion of the rotor and vanes to illustrate the theoryof operation.

The fan illustrated in the drawings comprises a casing 4 and a rotor orwheel 6 mounted on a shaft 8 which is joumaled in suitable bearings 10.The shaft is driven by a constant speed motor such as a squirrel cageinduction motor, preferably directly connected to the end 11 of shaft 8.On each side of the casing is an inlet cone or eye 12 through which theair passes from the atmosphere into the rotor 6. The casing is providedwith the usual outlet connection 14.

In order to control the output of the fan independently of the speed,each inlet cone is provided with a plurality of overlapping vanes 16. Asshown in Fig. 2, each vane is in the general shape of a sector and isprovided with pivot pins 18 and 20 at opposite ends. The outer pin 18 isjournaled in the inlet cone 12 and the inner pin 20 is jour- 1929,Serial No. 403,753

naled in a cone-shaped hub 22 secured to the bearing.

The vanes in each set are adapted to be simultaneously adjusted to anydesired inclination from closed position, as shown 'in Fig. 1, to openposition, as shown in Fig. 2. To this end, each pin 18 is journaled in ayoke 24 secured to the casing and each pin carries a bevel gear 26 whichmeshes with a bevel gear 28 mounted in a horizontal shaft 30 alsojournaled in the yoke. Secured to each gear 28 is a plate 32, theseveral plates on each side of the fan being connected by links 34 toform a closed ring about the inlet.

A coil spring 36 is provided connecting two of the plates at one pointin the periphery to take up lost motion in the mechanism.

To one of the gears is attached a plate 38 which, as shown in Fig. 1, isadapted to be similarly connected to the links 34 but which has anextension to which one end of an operating link 40 is attached. Thislink is connected at its other end to a-lever 42. The levers 42 onopposite sides of the fan are connected by a rock shaft 44. An arm 46which is adapted to be actuated to vary the position of the plate 38 andthereby to adjust the positions of the vanes is secured to the rockshaft. The arm 46 is shownin two positions in Fig. 1. In the full-lineposition, the vanes are completely closed. In the dot-and-dash lineposition, the vanes are wide open. The arm 46 may be adjusted manually,but in power plant operation is preferably operated by any suitablemechanism which functions on variations in the load.

It will be seen from Fig. 2, that the axes about which the vanes turn,although extending in a general radial direction from the shaft, areinclined somewhat from the vertical and therefore lie on the surface ofa cone. The purpose of this construction is'to afford sufficient spacenear the inner end of the vanes for the inner end mounting withoutunduly restricting the effective area of the inlet.

As shown in Fig. 2 and in the diagram of Fig. 3, the portion of eachvane on the inner or down stream side of its axis, that is, the sidenearer the fan, is of greater area than the outer or up stream portion.The ratio of areas is preferably about to 40, although the figure is notcritical. The purpose of thus unbalancing the areas is to permit openingand closing of the vanes with a minimum of effort.

In Fig. 3, there are shown two stream lines of be seen that because ofthe convergence of-the stream lines as the air enters between the vanes,

the velocity of air past the side of-each vane down stream from thepivot is much greater than its velocity past the up stream side. Thestatic pressure on the down stream side is therefore less than thepressure on the upstream side, and the tendency is for the vane to movetowards closed position. If the vanes are symmetrically pivoted,therefore, a considerable force is required to hold the vanes open inany desired position or to move them from closed to open position. Bymounting the vanes as shown in Fig. 2, with a preponderance of area onthe down stream side, the forces due to air pressure may beapproximately balanced so that only a small force is required to move orto hold the vanes.

As stated above, the best ratio has been found to be about 60-40,although it has been found that it may range from 70-30 to 55-45. Inthis range, the force required to move the vanes may be as little asone-fiftieth of the force required when the vanes are symmetricallymounted. When the down-stream area is less than 55% of the whole, theunbalance of forces increases very rapidly.

The fan of the present invention is particularly adapted for use asaforced draft fan which is operated by a constant speed motor. The actionof the spin velocity in permitting control of output without changingthe speed has been fully described in the patent referred to, but willbe briefly reviewed here.

Referring to Fig. 3, wherein the vanes are shown in nearly closedposition in solid lines, the air is admitted to the rotor in thedirection indicated by the arrow 50. The. velocity of the rotor isrepresented by the: arrow 52. It will be understood that for any usefulwork to be done on the fluid, there must be a relative velocity betweenthe fan and the entering fluid in the direction of rotation of therotor. When the vanes are nearly closed, the spin velocity representedby the vector 50 is not greatly diiferent from the velocity of the rotorand little work is therefore done by the rotor. When the vanes are inwide open position, as shown in dotted lines, the fluid enters in anaxial direction represented by the vector 54. The relative velocitybetween the wheel and the entering air is therefore considerable and themaximum output is then obtainable.

For intermediate outputs, the vanes are inclined to intermediatepositions.

In any case, the speed may be and preferably is maintained constant,thus permitting the fan to be driven by a squirrel cage induction motor,which has been found to be the most economical and satisfactory drivingmeans. The efllciency of this type of motor changes only a small amountwith reduced outputs.

It will be noted that just as in the fan of my above-mentioned patentthere is no appreciable throttling of the fluid even when the vanes arenearly closed. In any position of the vanes, the predominant controllingfactor is the spin velocity.

Having thus described the invention, what is claimed is:

1. A centrifugal fan comprising a rotor, a casing having an eye and asubstantially conical inlet passage leading to the eye, and a pluralityof vanes in the inlet pivoted on axes which are oblique to the rotoraxis and substantially at right angles to the conical inlet, the vanesbeing adjustable about their axes from substantially on the rotor axis,and a plurality of vanes pivoted on the hub and the conical inlet onaxes which are oblique to the rotor axis and substantially at rightangles to the conical inlet, the vanes being adjustable about their axesfrom substantially wide open position in which they do not appreciablyobstruct the flow of gas to the rotor through an angle of nearly 90degrees to a closed position, throughout which adjustment they directthe entering gas to the rotor with an appreciable spin, the work done bythe fan on the gas being variable in accordance with the adjustable spinintroduced by the vanes at diflerent posions.

3. A centrifugal fan comprising a rotor, a casing having an eye and asubstantially conical inlet passage leading to the eye, and a pluralityof vanes in the inlet pivoted on axes which are oblique to the rotoraxis and substantially at right angles to the conical inlet, the vanesbeing adjustable about their axes from substantially wide open positionin which they do not appreciably obstruct the flow of gas to the rotorthrough an angle of nearly 90 degrees to a closed position, throughoutwhich adjustment they directv the entering gas to the rotor with anappreciable spin, the work done by the fan on the gas being variable inaccordance with the adjustable spin in-' troduced by the vanes atdifferent positions, and means for simultaneously and uniformlyadjusting the vanes about their axes.

4. A centrifugal fan comprising a rotor, a casing having an eye and asubstantially conical inlet passage leading to the eye, a hub disposedon the rotor axis, and a plurality of vanes pivoted on the hub and theconical inlet on axes which are oblique to the rotor axis andsubstantially at right angles to the conical inlet, the vanes beingadjustable about their axes from substantially wide open position inwhich they do not appreciably obstruct the flow of gas to the rotorthrough an angle of nearly 90 degrees to a closed position, throughoutwhich adjustment they direct the entering gas to the rotor with anappreciable spin, the work done by the fan on the gas being variable inaccordance with the adjustable spin introduced by the vanes at differentpositions, and means for simultaneously and uniformly adjusting thevanes about their axes.

- HAROLD F. HAGEN.

